Oscillating coil for electrodynamic loudspeakers



Nov. 14, 1933. J, LEOPOLD 1,935,404

Y OSCILLATING COIL FOR ELECTRODYNAMIC LOUDSPEKERS Filed Feb. 19, 1952 INVENTOR JOACHIM LEOPOLD ATTORNEY Patented Ntv. 14,u 193.3

UNITED `STATES PATENT oFFicE j OSCILLATING COIL FOR ELECTRODYNAMI LOUDSPEAKERS tion of Germany Application February 19, 1932, Serial No. 594,021, and in Germany January 14, 1931 s claims. (ci. 17a-340)' 'The object of this invention is an oscillating coil for eleetrodynamic loudspeakers which compared with the forms of construction known in the earlier art distinguishes itself by special so- 5 lidity. As a result of such increased strength the coil form or supporting body of the coil can be made weaker, and as a result the requisite width of air-gap may be diminished. This in turn means the advantageous feature of greater sensitivity or responsiveness and higher eiciency.

A further object of the invention is to provide a voice coil device in which the coil form may be made very thin, thus permitting an air gap between the inner and outer pole pieces narrower than usual to be provided. In 'certain cases the voice coil form on which the coil is wound may be omitted entirely due to the arrangement and construction of the coil itself.

waste space between the successive turns.

cording to my invention this space is filled with conducting material in the shape of additional turns. of wire, so that I find it possible to sub= stantially ll (except for the small clearance re quired between the relatively moving parts) the air gap with useful coil turns.

A still further object is to arrange certain turns of the outer layer of a voice coil so that an outer turn puts radial pressure on or contacts two adjacent inner turns thereby serving tov restrain them from moving with respect to each other.

Other objects of the invention will appear as For an underthe description thereof proceeds.

`standing of the invention itself reference is made to the accompanying drawing in which,

Fig. 1 shows a coil form wound with wire of rectangular section;

Fig. 2 shows a coil form wound with wire of triangular section; and,

Fig. 3 shows one half of a coilwound with'wire of trapezoidal section; and,

Fig. 4 is an enlarged section'of two adjacent end turns of the coil of Fig. 2.

Known in the prior art are coils for which circular wire is used. However, this means a low utilizationy factor of the winding space due to the large Avolume taken up by interstices which remain between the constituent spires or turns. 'I'his disadvantage can be obviated by the use of wire of rectangular cross-section.

If in the case of such a winding the insulation were supposed to be absent then the constituent wires could be supposed-to be placed directly adjacent to one another without any spaces or interstices being incidentally formed as shown in Fig. 1. In this embodiment planes laidthrough the conductor strips are positioned at right anglesto the coil axis. Now, such coils involve the drawback that the forces coming to act upon the conductors tend to tear the joints asunder, as indicated in the drawing by the arrow. Now, the purpose `of this invention is to overcome this inconvenience. Y

According to this invention it is possible to increase the strength of the coil, this being accomplished by the aid of a profiled wire having a cross-sectional form other than circular, the wire cross-section being preferably so chosen and the wire itself being so wound that the constituent layers and turns will interengage. In such an arrangement the joints between turns will not be acted upon by the full force; indeed, owing to the slope only the corresponding force components. Another merit is that also the joints between the constituent turns and layers will no longer extend throughout the whole coil surface, but at the most some portion thereof. In other words, the chances of a break in the insulating layer produced at any given place extending through and affecting the whole coil resulting possibly in the entire coil being broken in two are thus diminished.

The two embodiments illustrated in Figs. 2 and 3 have proved of particularly great advantage. In the embodiment shown in Fig. 2 wire of trit angular cross-section is employed, the winding being so built that the triangular prole with one of its sides comes to be placed against and bear upon the cylindrical surface of the supporter body, while the apices located opposite those sides extend outwardly. In the next layer the triangles are positioned inversed, that is to say, the apices thereof thus coming to be placed between the spaces left in the first layer. The same arrangement is repeated if additional layers are provided.

The coil form C having axis E-F may be made of thin insulating material such as cardboard, paper or fabric and is carried by the inner end of -a large diaphragm D between the inner pole piece A and outer pole piece B of an electromagnet (not shown). The diaphragm D and electromagnet per se may be of the usual construction. The form C may be of cylindrical shape. Numerals 1, 2 and 3 denote successive turns of the inner layer; 4, 5 and 6 successive turns of the succeeding layer of winding; and 7, 8 and 9 successive turns of the next succeeding layer. will be understood that the wire conductor is coated with a/thin covering of insulating varnish or enamel as/ known to those skilled in the wire making arti" In winding the outer layer the wire is-preferably held taut or under tension, in which case turn 7 exerts an inward pressure against turns 1 and 4 and contacts with both said turns, thereby assisting in preventing turn 1 from moving endwise with respect to 4. If such motion occurred turn 1 may become loose and hit against 4 resulting in a clicking, objectionable noise.

Referring to Fig. 4 let OF represent the force exerted by turn 4 against turn. 1. This force /may be due to the inertia of turn 4- near the end of the path of motion of the voice coil or it may representthe force induced in turn 4 by the pas' separating from turn 4. In other words by shaping my wire to have inclined faces, I am enabled to use certain forces arising during the action of my device, which would otherwise be detrimental, to assist in securing its proper functioning.

In the embodiment shown in Fig. 3, wire of trapezoidal cross-section is used, in other Words the cross section is a trapezium having its inner and outer faces parallel to each other and in the claims the term trapezoid or trapezoidal is used in this sense. The mode of winding is substantially the same except that the wires placed in one and the same layer do not touch, but are separated from one another by the wires of the next layer. For instance, the procedure is such that first the wires 1, 2, and 3 belonging to the first layer are `wound first, and thereupon the wires 4 and 5 of the second layer are wound in the spaces, it being, of course, immaterial in what sequence the winding process proceeds so far as the invention is concerned. Instead of first accommodating the rst layer and in connection therewith the second layer, it is also feasible to 'lay both layers simultaneously by running the of coil shown in Fig. 3 as it does to that shown in Fig. 2.

Owing to the stabler disposition of the structure insured by a more favorable arrangement of the joints it is further possible to secure internal cohesionand solidity merely by the aid of insulation used on the wires. As a result the provision of a distinct support or bobbin is dispensable in some cases. Since the small insulation layers to replace the same and making it dispensable cannot be regarded as a supporting body inthe strict sense of the term, the basic idea of the present invention allows of the manufacture of unsupported coilsv which because of their little width and their high space utilization factor may be considered as the optimum form of construction of loudspeaker coils.

Having described my invention, what I claim 1.l -A voice coil comprising a winding of wire Ihaving a vsubstantially triangular cross-section,

edge inclined at an acute angle to the axis of said cylindrical form, whereby the force exerted by one turn on an adjacent turn produces a. radially exerted component thereon.

v4. A voice coil comprising a form, a winding of wire on said form the successive turns of said winding being spaced apart on said form by an amount substantially equal to the Width of said wire and other turns of said wire wound in the spaces provided between said first wound turns, said wire being of non-circular cross section.

5. A Voice coil comprising a form, a coil of wire wound on said form the cross section of said wire being non-circular, two adjacent turns of said Y winding having their outer edges in the same 12u plane and an outer turn wound in contact with each of said named turns and having its inner surface substantially fiat, thereby exerting a pressure on said two inner turns to retain them in position.

6. A wire, the cross sectional shape of which i is preformed into the shape of a trapezoid,lsaid wire being bent around a cylinder to form a coil, successive turns of said wire being spaced apart and other turns of the same cross-sectional shape interposed lbetween said first named turns.

JOACHIM LEOPOLD. 

